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8 - Saturn’s Ionosphere
- Edited by Kevin H. Baines, University of Wisconsin, Madison, F. Michael Flasar, NASA-Goddard Space Flight Center, Norbert Krupp, Tom Stallard, University of Leicester
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- Book:
- Saturn in the 21st Century
- Published online:
- 13 December 2018
- Print publication:
- 06 December 2018, pp 196-223
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Summary
This chapter summarizes our current understanding of the ionosphere of Saturn. We give an overview of Saturn ionospheric science from the Voyager era to the present, with a focus on the wealth of new data and discoveries enabled by Cassini, including a massive increase in the number of electron density altitude profiles. We discuss recent ground-based detections of the effect of “ring rain” on Saturn’s ionosphere, and present possible model interpretations of the observations. Finally, we outline current model-data discrepancies and indicate how future observations can help in advancing our understanding of the various controlling physical and chemical processes.
8 - Upper atmospheres of the giant planets
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- By Luke Moore, Boston University, Tom Stallard, University of Leicester, Marina Galand, Imperial College London
- Edited by Carolus J. Schrijver, Frances Bagenal, University of Colorado Boulder, Jan J. Sojka, Utah State University
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- Book:
- Heliophysics: Active Stars, their Astrospheres, and Impacts on Planetary Environments
- Published online:
- 05 March 2016
- Print publication:
- 17 March 2016, pp 175-200
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Summary
All celestial bodies are surrounded by gaseous envelopes, at least to some degree. When the gas is gravitationally bound to a parent body's nucleus it is called an atmosphere, whereas if the gas is not confined by gravity, such as at a comet, it is called a coma (Strobel, 2002). At one atmospheric extreme, such as Mercury or the Moon, the extremely tenuous atmosphere originating from the surface is referred to as a surface-bound exosphere, as the atmospheric atoms and molecules are much more likely to escape to space or to collide with the surface rather than collide with each other. At the other extreme, such as at the gas giants (Jupiter, Saturn, Uranus, Neptune), the rocky core about which the atmosphere is gravitationally bound is on the order of 0.1 planetary radii and gas constitutes the majority of the planet. A dense atmosphere is typically divided into two broad categories: the lower and upper atmospheres. The study of the lower regions (troposphere and stratosphere) forms the discipline of meteorology, while the study of the upper regions (mesosphere, thermosphere, exosphere) and their ionized component (ionosphere) forms the discipline of aeronomy.
Atmospheres play vital roles in planetary and satellite evolution, as they help to insulate the surface of a body from external influences. In particular, the upper atmosphere represents a key transition region between a dense atmosphere below and a tenuous space environment above. An array of complex coupling processes from below, such as waves, and from above, such as forcing by solar extreme ultraviolet (EUV) photons and energetic particles, means that aeronomy deals with the highly coupled system of neutrals, plasmas, and electromagnetic processes that link planets, moons, and comets from their surfaces to their magnetospheres, to the solar wind, and ultimately to the Sun itself (Mendillo et al., 2002).
Evidence of these coupling processes include various upper-atmospheric emissions, such as dayglow and nightglow, resulting from the absorption of solar photons, and aurorae, which are produced by the energy deposition of energetic particles from the space environment. Such emissions can be detected remotely, and have consequently allowed detailed study of the planets in the solar system. In addition to a host of ground-based observations, a number of spacecraft have also been used to study the giant planets.
The science of EChO
- Giovanna Tinetti, James Y-K. Cho, Caitlin A. Griffith, Olivier Grasset, Lee Grenfell, Tristan Guillot, Tommi T. Koskinen, Julianne I. Moses, David Pinfield, Jonathan Tennyson, Marcell Tessenyi, Robin Wordsworth, Alan Aylward, Roy van Boekel, Angioletta Coradini, Therese Encrenaz, Ignas Snellen, Maria R. Zapatero-Osorio, Jeroen Bouwman, Vincent Coudé du Foresto, Mercedes Lopez-Morales, Ingo Mueller-Wodarg, Enric Pallé, Franck Selsis, Alessandro Sozzetti, Jean-Philippe Beaulieu, Thomas Henning, Michael Meyer, Giuseppina Micela, Ignasi Ribas, Daphne Stam, Mark Swain, Oliver Krause, Marc Ollivier, Emanuele Pace, Bruce Swinyard, Peter A.R. Ade, Nick Achilleos, Alberto Adriani, Craig B. Agnor, Cristina Afonso, Carlos Allende Prieto, Gaspar Bakos, Robert J. Barber, Michael Barlow, Peter Bernath, Bruno Bézard, Pascal Bordé, Linda R. Brown, Arnaud Cassan, Céline Cavarroc, Angela Ciaravella, Charles Cockell, Athéna Coustenis, Camilla Danielski, Leen Decin, Remco De Kok, Olivier Demangeon, Pieter Deroo, Peter Doel, Pierre Drossart, Leigh N. Fletcher, Matteo Focardi, Francois Forget, Steve Fossey, Pascal Fouqué, James Frith, Marina Galand, Patrick Gaulme, Jonay I. González Hernández, Davide Grassi, Matt J. Griffin, Ulrich Grözinger, Manuel Guedel, Pactrick Guio, Olivier Hainaut, Robert Hargreaves, Peter H. Hauschildt, Kevin Heng, David Heyrovsky, Ricardo Hueso, Pat Irwin, Lisa Kaltenegger, Patrick Kervella, David Kipping, Geza Kovacs, Antonino La Barbera, Helmut Lammer, Emmanuel Lellouch, Giuseppe Leto, Mercedes Lopez Morales, Miguel A. Lopez Valverde, Manuel Lopez-Puertas, Christophe Lovi, Antonio Maggio, Jean-Pierre Maillard, Jesus Maldonado Prado, Jean-Baptiste Marquette, Francisco J. Martin-Torres, Pierre Maxted, Steve Miller, Sergio Molinari, David Montes, Amaya Moro-Martin, Olivier Mousis, Napoléon Nguyen Tuong, Richard Nelson, Glenn S. Orton, Eric Pantin, Enzo Pascale, Stefano Pezzuto, Ennio Poretti, Raman Prinja, Loredana Prisinzano, Jean-Michel Réess, Ansgar Reiners, Benjamin Samuel, Jorge Sanz Forcada, Dimitar Sasselov, Giorgio Savini, Bruno Sicardy, Alan Smith, Lars Stixrude, Giovanni Strazzulla, Gautam Vasisht, Sandrine Vinatier, Serena Viti, Ingo Waldmann, Glenn J. White, Thomas Widemann, Roger Yelle, Yuk Yung, Sergey Yurchenko
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- Journal:
- Proceedings of the International Astronomical Union / Volume 6 / Issue S276 / October 2010
- Published online by Cambridge University Press:
- 10 November 2011, pp. 359-370
- Print publication:
- October 2010
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The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?
In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life.
The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.
EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates.
Aurora on Jupiter: A Magnetic Connection with the Sun and the Medicean Moons
- Supriya Chakrabarti, Marina Galand
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- Journal:
- Proceedings of the International Astronomical Union / Volume 6 / Issue S269 / January 2010
- Published online by Cambridge University Press:
- 03 November 2010, pp. 71-79
- Print publication:
- January 2010
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Observational astronomy began in Padova four hunderd years ago, when Galileo Galilei pointed a newly invented instrument towards Jupiter. After only one week of observations he discovered four moons circling Jupiter. In the intervening four centuries, technical progress in instrumentation and novel observational approaches have revealed much about the connection between these Medicean moons with Jupiter, none more revealing than the auroral emissions. In this paper we review observations of ultraviolet aurora made by earth-orbitting spacecraft as well as those that flew by the Jovian system.